Summary
We propose to adopt a new airworthiness directive (AD) for certain Air Tractor, Inc. (Air Tractor) Model AT-602 airplanes. This proposed AD would require you to install access holes to do repetitive detailed visual inspections for cracks in the horizontal stabilizer brace tube assembly, and if any cracks are found as a result of a visual inspection, to replace the horizontal stabilizer brace tube assembly with a new design horizontal stabilizer brace tube assembly. The installation of the new design horizontal stabilizer brace tube assembly is terminating action for the repetitive inspection requirement. This proposed AD results from two reports of Model AT-602 airplanes with cracked horizontal stabilizer brace tube assemblies. We are proposing this AD to detect and correct cracks in the horizontal stabilizer brace tube assembly, which could result in failure of the horizontal stabilizer. This failure could affect the ability to control pitch with consequent loss of control.